Ronnie Hillman and Montee Ball are having their growing pains in Denver Broncos backfield

Ronnie Hillman and Montee Ball stood out for all the wrong reasons last weekend.

Denver's young running backs want to atone for their big blunders when the Broncos host the St. Louis Rams on Saturday night in what's essentially the final dress rehearsal for the regular season.

Hillman fumbled when he tried to stretch the ball over the goal line on second down from the 1, and Seattle cornerback Brandon Browner returned it 106 yards for a touchdown that set the tone for the 40-10 thumping by the Seahawks.

Worse, Ball whiffed on a Seahawks blitzer and allowed Peyton Manning to get creamed.

One gaffe cost them a touchdown; the other could have cost them the season.

"I don't know about dog house. I don't really have a dog house," coach John Fox said, "but they'll improve and they're young players and that's what you expect."

The Broncos are enduring some growing pains with their two young running backs after releasing veteran Willis McGahee in the offseason.

"It's like anything, the more you do it the better you get, and they're working hard," Fox said. "They're doing great in meetings; they're doing great in practice. They'll continue to get better each week in games and they're making progress."

Hillman has gained 43 yards on 16 carries in the preseason for a 2.7-yard average. Ball has 37 yards on 11 carries for a 3.4-yard average.

Neither has reached the end zone, although Hillman was certain he'd stuck the football over the goal line before it popped loose in Seattle.

"You don't want to even reach the ball over on first, second or third down — only on fourth down," Manning said. "That's something he'll learn from."

Hillman's fumble was one of three in the first half that infuriated offensive coordinator Adam Gase, who made turnovers "a huge point of emphasis for us this offseason" because they led to a 2-3 start last year.

Ball knows that to get onto the field he can't allow clean shots on Manning like the one Seahawks middle linebacker Bobby Wagner got just as Manning was releasing a pass to tight end Julius Thomas that was good for 31 yards.

"I got a piece of him and he slipped off me at the last second," Ball said. "I'll correct that, and we'll move forward."

Manning's head bounced off the ground but no flag was thrown. Two plays later, Manning threw an 11-yard TD pass to Wes Welker, and the Broncos used a few more two tight-end sets to better protect him after that.

Asked what was more important for running backs, pass protection or ball security, Gase didn't hesitate: "I'd say both are equally as important."

"When the ball is in your hand it can't be on the ground. What happened the other day? I'm telling you, unacceptable. It's not going to happen; it's not going to happen anymore. We're not going to put the ball on the ground, or else they're not going to carry it," Gase said. "In pass protection, their job is to make sure 18 doesn't get touched, and that's what they're going to do."

Or they're not going to get onto the field.

The Broncos want to put wide receivers Welker, Demaryius Thomas and Eric Decker on the field together along with tight end Julius Thomas, who isn't their best blocker but shows enormous potential as a pass-catcher — he leads the team with eight catches for 105 yards in the preseason.

But to get those four on the field, they'll need a running back that can pick up the blitz so they don't have to send in another blocking tight end to replace one of Manning's targets.

That's where fifth-year veteran Knowshon Moreno might come in.

Gase said Moreno has taken on some of the veteran leadership duties that McGahee used to provide.

"He's done a good job of helping the younger guys," Gase said. "I would say his ability in pass protection to explain some things, when we get out on the field, he's seen more than the two young guys. And he does a good job of explaining those things. He can communicate with them really well."

He also can lead by example, and although he looks like an insurance policy right now as the third-string running back, he could very well end up getting significant snaps if Hillman and Ball continue to make mistakes.